One earlier known method for maintaining the spark plugs of an internal combustion engine free from deposits involves the repeated generation of sparks between the spark plug electrodes.
The U.S. Pat. No. 4,341,195 teaches an ignition system in which, under certain engine conditions and when running of the engine has become established, a spark discharge is generated continuously across the plug with the aid of a specific ignition circuit. The number of discharges generated is inversely proportional to the speed of the engine and proportional to the engine load.
The U.S. Pat. No. 4,024,469 teaches an arrangement in which the plug gap is measured by means of a measuring system which is connected to an ignition system and which applies a high alternating voltage across the plug, so as to burn-off deposits present thereon.
The German Patent Specification No. 26 45 226 describes an ignition system with which a thin-walled precombustion chamber is heated, by repeatedly effecting an electrical discharge across the spark plugs. For the purpose of facilitating an engine start in cold and moist conditions, arrangements have also been proposed for heating the actual spark plugs with the aid of a direct current; cf. for instance U.S. Pat. No. 3,589,348.
This prior art has presented complicated solutions which require the provision of numerable ancillary devices and components additional to the conventional ignition system. In some cases the ignition system has been incapable of burning-off carbon deposits effectively, particularly in difficult engine start conditions.